Marcus Aurelius Antoninus, better known by his nickname Caracalla, was Roman emperor from 198 to 217 AD. He was a member of the Severan dynasty, the elder son of Emperor Septimius Severus and Empress Julia Domna. Proclaimed co-ruler by his father in 198, he reigned jointly with his brother Geta, co-emperor from 209, after their father's death in 211. His brother was murdered by the Praetorian Guard later that year under orders from Caracalla, who then reigned afterwards as sole ruler of the Roman Empire. Caracalla found administration to be mundane, leaving those responsibilities to his mother. Caracalla's reign featured domestic instability and external invasions by the Germanic peoples.

The Roman emperor was the ruler and monarchical head of state of the Roman Empire, starting with the granting of the title augustus to Octavian in 27 BC. The term "emperor" is a modern convention, and did not exist as such during the Empire. Often when a given Roman is described as becoming emperor in English, it reflects his taking of the title augustus and later basileus. Another title used was imperator, originally a military honorific, and caesar, originally a surname. Early emperors also used the title princeps alongside other Republican titles, notably consul and pontifex maximus.